This invention is directed generally to fluid warming apparatus and, more particularly, to a device and method for measuring the operating temperature of apparatus for warming cold parental fluids such as whole blood for intervenous injection or transfusion procedures.
Whole blood is commonly stored in blood banks at a temperature of 4.degree. C until infused into a patient, at which time it is necessary that the blood be warmed to or slightly below the 37.degree. C temperature of the human body if hypothermia and the attendant risk of ventricular fibrillation and cardiac asystole are to be avoided. For applications where substantial and unpredictable quantities of blood are required, as where a patient hemorrages during surgery, it is preferable that blood in storage be transferred substantially directly into the patient, since this avoids warming blood which is not subsequently used.
The apparatus described in the copending application of Robert J. Froehlich and Daniel B. Granzow, Jr., Ser. No. 761,926, concurrently filed herewith, provides an effective and efficient system for dry warming blood or other parental fluids to body temperature during the process of infusing such fluids into the patient. It is a feature of that invention that the temperature of the infused blood is maintained substantially constant at 37.degree. C substantially independent of flow rates, which may vary from 0 to 150 ml per minute depending on the needs of the patient. A further feature is that the operation of the apparatus, as well as the temperature of the blood leaving the apparatus, is continuously monitored, and in the event of a malfunction operation is terminated and an alarm is sounded. Novel self-test provisions within the apparatus allow the operator to verify the operation of these monitoring circuits prior to placing the blood warming apparatus in service.
Sterility of the blood is maintained and contamination of the apparatus is avoided by use of a disposable flow system having a blood warming bag which fits within the apparatus in thermal communication with electric heating elements. An additional feature of that invention provides an alarm in the event of inadvertent removal of the blood processing bag from the apparatus, and AC-coupled sensing circuitry which measures the temperature of the blood at the inlet and outlet portions of the blood processing bag automatically controls the operation of the heating elements to more accurately maintain the output temperature of the blood.
However, the need exists for means to independently measure the operating temperature of such apparatus, both to verify its proper operation, and to facilitate adjustment of its control circuits. Preferably, such temperature measuring means should be convenient and simple to use, and should provide an accurate reading completely independent of the warming apparatus.
Accordingly, it is a general object of the present invention to provide a new and improved method and apparatus for measuring the operating temperature of apparatus for warming blood and other parental fluids prior to infusion into the human body.
It is another object of the present invention to provide a method and apparatus for measuring the operating temperature of apparatus for warming blood and other parental fluids which is simple and convenient to use, and which provides an accurate measurement completely independent of the warming apparatus.